We have recently described the partition of wheat germ agglutinin (WGA) receptor sites over the protoplasmic and exoplasmic plasma membrane faces of freeze-fractured human thymus-derived (T) lymphocytes. Our results indicated there is an heterogenous expression of integral membrane proteins (receptor sites over protoplasmic faces) within populations of human T cells. Here, we look for the distribution of WGA receptor sites over fracture-faces of the plasma membranes of neoplastic lymphocytes. We observed that, in cells from the culture lines Molt 4 (from acute lymphoblastic T leukemia) and Hut 78 (from mycosis fungoides), exoplasmic fracture-faces were always labeled, but no WGA receptor site was found on protoplasmic fracture-faces.